The basic principle in application is to know whether the passage is a statement of the law or of the gospel. For when the Word is preached, the law and the gospel operate differently. The law exposes the disease of sin, and as a side-effect stimulates and stirs it up. But it provides no remedy for it. However the gospel not only teaches us what is to be done, it also has the power of the Holy Spirit joined to it. When we are regenerated by him we receive the strength we need both to believe the gospel and to do what it commands. The law is, therefore, first in the order of teaching; then comes the gospel.  – William Perkins